1. Field of the Invention
The invention relates to a technology whereby a temperature of a region in which no temperature sensor is installed is estimated.
2. Description of Background
In measuring temperatures, temperature sensors are commonly used. However, there is a case where it is necessary to check the temperature of a region in which no temperature sensor can be installed directly. Moreover, the probability of the temperature sensor failure is likely to become higher as the number of the sensors increases. Accordingly there are cases where the number of the temperature sensors is desired to be decreased as much as possible. For such cases, it has become the practice to measure a physical value other than the temperature and to estimate the temperature on the basis of a temperature dependence of the physical value. For example, Japanese Patent Laid-Open Publication No. 7-2344162 discloses a technology where a forward current and a forward voltage of an IGBT (insulated gate type bipolar transistor) are measured, and the temperate of the IGBT is estimated from the temperature dependence of the current-voltage characteristics thereof.
Moreover, there are cases where, although the temperature sensor was installed, the temperature at a region in which the temperature sensor was installed is estimated by another means, to detect its malfunctioning. For example, Japanese Patent Laid-Open Publication No. 10-62266 discloses a technology where, in order to detect malfunctioning of a thermistor for measuring a coil temperature of a motor, the coil temperature is estimated by another means. In this technology, a resistance of the coil is obtained from the inductance and the current value of the coil, and the coil temperature is estimated from the temperature dependence of the resistance.
In the temperature estimation technology described above, a specified physical characteristic concerning a region whose temperature is to be estimated is measured and then the temperature is estimated on the basis of the temperature dependence of the physical characteristic. For such a physical characteristic, one that shows a distinct temperature dependence is used.
However, depending on the kind of the region to be estimated, there may be a case where a physical characteristic showing a distinct temperature dependence cannot be measured. Or there may be a case where, although the measurement of such a physical characteristic is feasible, its measurement is not desired because of the need to reduce the number of sensors. Due to various circumstances such as those, there is desired a technology whereby the temperature can be estimated by means other than a method of directly using the temperature dependence of a physical characteristic of the region whose temperature is to be estimated.